Conventionally, an image-region segmentation apparatus for segmenting an input image into achromatic regions and chromatic regions by using saturations and hue differences has been known (Japanese Unexamined Patent Application Publication No. 6-259549).
This image-region segmentation apparatus includes an image input section, a normalization processing section, a saturation detecting section, a hue-difference detecting section, a feature determining section and a digitization processing section. The image input section receives a color image, generates a target image that is subjected to region segmentation on the basis of the received image, and outputs an R image, a G image, and a B image showing R (red) components, G (green) components, and B (blue) components of the target image to the normalization processing section.
The normalization processing section receives the three R image, G image, and B image output from the image input section. With respect to individual pixels of the target image, the normalization processing section converts the R, G, and B components into X components and Y components normalized according to brightness. The normalization processing section then generates an X image, in which pixel values of the target image are the X components, and a Y image, in which pixel values of the target image are the y components, and outputs the generated X image and Y image to the saturation detecting section and the hue-difference detecting section.
The saturation detecting section receives the X image and Y image output from the normalization processing section, determines the saturations of the individual pixels of the target image on the basis of the X components and Y components, outputs, to the feature determining section, a saturation image in which the values of the pixel values of the target image are represented by the determined saturations. The saturation Sk of the pixel Pk (k=1, 2, . . . , N) of the target image is determined by Sk=(xk2+yk2)1/2, where xk indicates the X component of Pk and yk indicates the Y component.
The hue detecting section receives the X image and Y image output from the normalization processing section, determines the hues of the individual pixels of the target image on the basis of the X components and the Y components, and determines a hue difference between the hues and a hue θc of a chromatic region. The hue detecting section then outputs, to the feature determining section, a hue-difference image in which the value of each pixel value of the target image is represented by the determined hue difference. A hue θk of the target image Pk is determined by θk=tan−1 (yk/xk).
Upon receiving the saturation image from the saturation detecting section and receiving the hue-difference image from the hue detecting section, the feature determining section determines features from the saturation and hue difference of each pixel. For example, the feature determining section determines features Fk of the pixel Pk of the target image by using Fk=Sk cos (θk−θc). The feature determining section then outputs, to the digitization processing section, a feature image in which the value of each pixel of the target image is represented by the determined features Fk.
Upon receiving the feature image from the feature determining section, the digitization processing section digitizes the feature image. Of the two regions segmented by the digitization, the digitization processing section outputs a region having smaller features as an achromatic region and outputs a region having larger features as a chromatic region.
As described above, the conventional image-region segmentation apparatus uses the saturation at each point in an input image and a hue difference between the hue at each point in the input image and the hue of a chromatic region, to determine features for segmenting the input image into achromatic regions and chromatic regions, and uses the determined features to segment the input image into achromatic regions and chromatic regions.